Katie is continuation of the Qt4 C++ toolkit with the goal to keep it alive,
clean it up, fix some bugs and backport some features from Qt5. It is based
on the latest Git revision of Qt v4.8.

There are several things you should be aware before considering Katie:

 - some components and tools have been removed:
  - QMake, Linguist, Assistant, checksdk, macdeployqt, pixeltool, qconfig,
    qdoc, qev, qvfb, runonphone and other non-essential
  - Qt3Support, QtWebKit, ActiveQt and Phonon

 - some things have changed:
  - QMake build system replaced with CMake
  - QStyleOption*V{2,3,4} classes have been merged
  - QKeyEventEx and QKeyEvent classes have been merged
  - OpenSSL and D-Bus cannot be runtime dependencies, they must be linked to
    during build
  - QtUiTools is build as shared library by default
  - updated bundled Harfbuzz from upstream (not Harfbuzz-NG)
  - Symbian, QWS and QPA are no longer supported platforms
  - OpenVG is no longer supported graphics output
  - QML debugger and inspector have been removed, potentially dangerous
  - removed non-open source DB2, OCI and TDS database drivers
  - removed 3rd party sources that are very common nowdays

 - some additions have been made: 
  - JSON classes and types
  - command line parser
  - standard directories handler
  - building against IODBC instead of unixODBC is possible
  - alternative libc implementations support

Bugs fixed in Katie, some of which in Qt5 too:
QTBUG-23502, QTBUG-37115, QTBUG-15052, QTBUG-23522, QTBUG-6139, QTBUG-26889,
QTBUG-21548, QTBUG-6133, QTBUG-18188, QTBUG-36767, QTBUG-35387, QTBUG-37035,
QTBUG-28321, QTBUG-21993, QTBUG-26590, QTBUG-2124, QTBUG-20482, QTBUG-41361,
QTBUG-40153, QTBUG-35479, QTBUG-1628

Unless you use QMake and QDoc porting to Katie or even supporting it along with
Qt4 in the same codebase is trivial and requires only minor changes because
Katie is mostly source compatible with Qt4. Should you enouncter a problem
please report it at https://github.com/fluxer/katie/issues.